MELBOURNE, Australia — Gay rights advocates argued in Australia’s highest court on Tuesday that the government does not have the power to bypass Parliament to pay for a 122 million Australian dollar ($97 million) public survey on whether gay marriage should be legalized.

The advocates want Parliament to decide the issue without consultation with the public and argued in the High Court that the government does not have the constitutional power to start the postal survey next week.

The government will argue its case on Wednesday.

Opinion polls show that most Australians want same-sex marriage legalized, but many advocates question how representative of Australian attitudes the postal survey would be.

The seven judges are hearing two similar cases simultaneously over Tuesday and Wednesday in the city of Melbourne. The judges could rule on the validity of the survey as early as Wednesday and prevent ballots being posted to voters from Sept. 12.

The survey is the second choice of Prime Minister Malcolm Turnbull’s conservative government, which had promised a rare, compulsory vote known as a plebiscite.

But the Senate refused to approve the AU$170 million that that vote on Nov. 25 would have cost.

So the government is pushing for a voluntary postal vote without Senate approval at a cost of AU$122 million.

If a majority wants marriage equality, Parliament would be allowed to decide the issue by December. But some lawmakers have said their votes in Parliament would not be swayed by public opinion, raising questions about why the public is being surveyed.

Lawyer Ron Merkel told the court Tuesday that the government’s power to fund such a vote without Senate approval can only be used in unforeseen emergencies. Merkel said there was no urgent need to hold the postal survey.

If the court stops the survey, lawmakers in the minor Greens party are pushing for a bill to legalize gay marriage to be introduced to the Senate next week.